The present invention relates to a novel method and apparatus for strain amplification for piezoelectric transducers. Specifically, the invention relates to strain amplification by elevating the piezoelectric crystal above the neutral axis of the plate by castellations formed on the plate.
The measurement of strain is accomplished using a piezoelectric crystal mounted on a supporting plate which is attached to a base which communicates with a structure to be monitored. In the typical case, the crystal is mounted on a so-called xe2x80x9cunimorphxe2x80x9d supporting plate which is attached in direct contact over substantially the entire surface of the piezoelectric crystal. It has long been well known to make such unimorph transducers using piezoelectric materials. It has also long been well known that single crystal piezoelectric materials could be used in such unimorph transducers. However, the sensitivity of such a transducer structure is limited by the physical dimensions and material properties of the sensing components of the transducer. It is therefore desirable to improve the sensitivity for a transducer of a given class or application without changing the overall physical dimensions of the transducer.
The present invention addresses the shortcomings of the existing piezoelectric transducers and provides improved sensitivity for a given application by providing a transducer configuration which amplifies the strain for a transducer otherwise having the same given physical dimensions and made up of the same given transducer materials. This is accomplished by a transducer having a mounting plate for mounting the piezoelectric crystal in which the mounting plate has raised protrusions which offset the crystal from the surface of the mounting plate. In profile, these protrusions resemble the gun placements of a castle turret and hence are referred to herein as xe2x80x9ccastellations.xe2x80x9d The castellations produce significant increases in sensitivity. Circular or waffle pattern castellations are specifically shown, although other configurations are contemplated.
The devices which utilize the method and apparatus of the present invention (for example, accelerometers, velocity sensors, impedance heads, and hydrophones) exhibit a higher charge sensitivity and resonance frequency than existing transducers. These advantages extend the number of applications and efficacy of the devices. It is the purpose of this invention to provide a predictable and hitherto unattained quality factor as is defined herein. Moreover, the simplicity of the design and micromachined, photoetched castellated components contribute to a low cost of manufacturing not evidenced in the existing transducers. This is achieved by using the castellated surface on which the piezoelectric transducer is mounted.